Disk drive technology has undergone rapid and substantial improvements over time. These improvements have led to increasing use of high density hard disk drives and the like in a wide range of devices. Such devices include, for example, MP3 players, cellular phones, personal organizers, cable boxes, video recorders, and automotive systems, as well as more conventional devices associated with disk drives, such as computers, microcontrollers, embedded controllers, and the like.
Consumer expectations as well as industrial requirements have placed a substantial burden on disk drive designers to increase the performance of such drives. One manner in which performance of the drive may be increased is by reducing the time required for the drive to spin-down from its operating rotation rate. Another manner in which performance of the drive may be increased is by reducing the time required for the drive to spin-up to its operating rotation rate after the disk drive has received a spin-down command.
Conventional disk drive systems include a storage medium that is rotatably driven by a spindle motor. Such disk drive systems often use back EMF detection to determine the position of the spindle motor during spin-up and spin-down operations. Since sensing of the spindle motor position using back EMF detection is difficult, if not impossible, when the disk is rotating slowly, most spin-down operations are implemented by simply waiting for a certain calculated time to elapse thereby allowing sufficient time for the disk to stop rotating before a spin-up operation is executed. The calculated time may be based on a number of factors including the torque constant Kt of the spindle motor. Once this waiting time has been calculated, it is used for all spin-up and spin-down operations and becomes a fixed constant used by the disk drive system.
Improvements in spin-up and spin-down disk drive operations may be achieved if the latency introduced by the fixed waiting time is reduced or eliminated. Reduction or elimination of the fixed waiting time may be achieved through real-time spindle motor rotation sensing. Implementing such real-time sensing in an economical manner, however, can be a significant challenge.